Apparatus for extruding metal



April e, 1937. R. HORLEY 2,076,199

APPARATUS FOR EXTRUDING METALy Filed Sept. 27. 1934 5 Sheets-Sheet 2 April 6, '1937- Rui-:.HoRL-EY 2,076,199

APPARATUS FOR EXTRUDING METAL I April 6, 1937.

R. E. HORLEY APPARATUS' FOR EXTRUDING METAL Filed Sept. 27, 1954 5 Sheets-Sheet 5 1 #Zier/very Patented Apr. 6, 1937 UNITED STATES vPATENT OFFICE 2,076,199 APPARATUS FOR EXTRUDING BIETAL Robert Eustace Horley, London, England, assignor to Pirelli-General Cable Works Limited, London, England, a British Application september 27, 1934, serial No. 745,810 In Great Britain October 9, 1933 16 Claims.

of lead or lead alloys, or rods, or other continuous solid sections of metal; the apparatus used is of the kind comprising inner and outer longitudinally extending and relatively rotatablecoaxial members, one of which forms the working chamber into which the metal is fed at one end in a molten state and through which the metal, under the action of the other member, is driven forward and nally extruded through a suitably shaped die or dies at the other end of the chamber in the form of a bar, pipe or cable sheath. In known apparatus of this type one of the above relatively rotatable members was provided with a screw thread so as to constitute the impellingv device, whilst the surface of the other member facing the screw thread was formed with longitudinal ribs or grooves parallel to the axis of rotation or with helical threads, ribs or grooves opposite in twist or inclination to those on the screw-threaded impeller; the object of these ar- 2 rangements was to prevent rotation of the metal helix that is formed in the spaces between the convolutions of the screw impeller while allowing the said metal helix and the metal in the grooves to slide towards the die chamber, and

for this purpose it was deemednecessary to impose :is-little shear stress as possible on the metal keys that result from the configuration of the.

surface of the member referred to above as complementary to the screw impeller, so that these keys remain substantially integral with the metal between the convolutions of the impeller.

In contradistinction to the above action, in the method according to the present invention the metal in the keyways or recesses formed in the member complementary to the screw impeller,

instead of being allowed to proceed toward the' die chamber, remains substantially stationary, being retained in the said keyways or recesses, and serves to restrain rotation of the metal in the convolutions of the screw impeller by frictional contact therewith. In other Words, the Y shear stress to which the metal keys are subjected, instead of being minimized as in previous methods, is increased to the point at which shear actually occurs due to the impelling action of the screw, owing to the fact that the metal in the keyways or recesses is not allowed to move forward. In comparison with the above-mentioned earlier proposals, whereby,A V'under the most favourable conditions, only a comparatively low output was obtainable, apparatus operating on the present principle is capable of a materially increased output.

For this purpose there is employed according to the present inventiomfor the continuous extr'usion of metal pipes or cable sheaths or solid articles, an apparatus of the kind comprising inner 'and outer longitudinally extending and relatively rotatable concentric members, one of which forms the working chamber, and the other is provided with a screw thread so as to form a screw impeller. In a preferred form of construction the outer member is the working chamber and is stationary and its inner surface is provided with grooves or projections or recesses of such dimensions and shape as permit of eX- trusion by thel above-described novel method. The inner member has on its outer surface the screw thread and rotates and on rotating produces complete rupture by shear between the metal, such as lead, which fills the grooves or spaces between the projections lor recesses of the working chamber andthe metal helix formed between the convolutions of the screw impeller. The metal filling the said grooves or spaces or recesses remains substantially firmly 4iixed therein and possesses the requisite mechanical strength to restrain rotation of the aforementioned metal helix by frictional contact therewith. Alternatively, the inner surface of the stationary working chamber may be provided with a screw thread and the outer surface of the inner revolving member with grooves, projections or recesses.

The invention is illustrated by way of. ex-

ample in the accompanying drawings,.wherein:-

, Figure 1 is a longitudinal section of the more important members of an extrusion4 apparatus suitable for sheathing cables,

Figure 2 depicts in longitudinal section a portion of the outer member of the extrusion apparatus, the screw impeller being removed. A v

Figure3 is an end view of the outer member shown in Figure 2,

Figures 4 and 5 are respectively longitudinal troduced from the rear of the apparatus through Referring to Figures 1 to 3, the outer member I constituting the working chamber is internally of cylindrical form and is fitted with an impeller member 2 rotated in any suitable manner and formed on its external surface with a series of helical grooves 3. In the apparatus illustrated the complementary recesses 4 in the outer member I are in the form of a draught-board pattern, the recesses being square and alternating with raised portions 5, as seen most readily in Figures 2 and 3. The screw impeller 2 does not completely flll the interior of the working chamber I, a space 6 constituting the die chamber being left at the right-hand end as seen in Figure 1. Within this space there is located a conical die 1 screwed into and rotating with the impeller 2. The base of this die is formed witha squared aperture 8 so that it may be screwed into position or removed by means of a long bar Spanner ina tubular member 9. Co-operating with the con- Ying effect in these localities.

ical die 1 is a ring die which is preferably, as illustrated,r in British patent specification, No. 418,078. This comprises a main ring die I8 secured by a nut II, within which die there is located an auxiliary ring die I2, the position of which in the axial direction is adjusted by means of a hollow nut I3. The cable to be sheathed is fed through the tubular member 9 and on passing out of the apparatus through the hollow nut I3 is covered with a sheath of lead, lead alloy or other suitable material supplied to the die chamber 6 by means of the screw impellerl, the thickness of the sheath being determined by the adjustment of the auxiliary ring die I2.

'The metal to be extruded is fed in a molten condition from a melting pot, not shown, through a duct I4 in the outer member I. The molten metal has direct access to the helical grooves 3 which are, therefore, fllled with metal'and from which the metal finds its way into the recesses 4 in the outer member. In these it solidiles and is then sheared oil! from the metal in the helical grooves 3 so that, as above described, the recesses 4 become more or less permanently lled with metal in the solid or semi-solid state; this metal exerts sufficient drag on that in the helical grooves 3, by virtue of its frictional superficial contact therewith, to restrain it from rotation and cause it to be impelled into theA die chamber 6 and finally extruded between thedies I and I2.

In order that in the various parts of the apparatus the metal may be maintained in the necessary molten, plastic or solid state, heating and cooling means are provided. In 'the example illustrated the former is constituted by a series of ring-shaped gas burners I5 encircling the apparatus and adapted to direct their llames on to it. As above mentioned. supply of heat is required in the neighbourhood of the inlet duct I4, in the die chamber 6 and also` centrally of the working chamber formed by the outer member I. Accordingly, as indicated, the gas, oil or other fuel burners I5 are so placed as to exert their heat- Equally well the heating elements I5 may be constituted as electrical resistance coils. Cooling means is constituted by jackets I6 formed in the outer member I, provision being made whereby a suitable `cooling medium such as water, steam, oil or air may be circulated in these jackets. By regulation vof the heating and cooling effects contributed respectively by the gas burners and cooling jackets I6, great variation of temperature regulation may be secured, thus making it possible to use the apparatus for the extrusion of metals of widely different characteristics. It may also be desirable prevents undue rise in the temperature of the cable to be sheathed; further, in the sheathing of an oil-impregnated cable, cooling may be effected by circulating oil between the cable itself and the tubular member 9.

It will be understood that, while in the example illustrated in Figures 1,2 and 3 the recesses 4 are fashioned to the form of a vdraughtboard, any other suitable shape of recess may be adopted, provided that it is such as to ensure that in operation the method constituting the essential feature of the invention. shall be followed, namely, that the recesses shall become more or less permanently filled with metal which vis sheared off from the metal occupying `the convolutions of the screw impeller, the rotation of which metal is restrained by frictional contact with the metal in the recesses. For example, the recesses 4 might take the form of a series ofcontinuous or intermittent helical grooves of the same hand as the grooves 3 around the impeller 2. Alternatively, the grooves may extend in the longitudinal direction parallel to the axis of the impeller 2.

In the apparatus depicted in Figures 4 and 5, the outer member I, constituting theworking chamber, is fitted with three screw impellers 2a which, however, feed into a common die chamber 6*' whence the metal is extruded, as in the previously described apparatus, between conical and ring dies 1EL and IIl. rI'hese impellers have helical grooves 3 therein. In this instance the recesses 4 take the form of longitudinal grooves parallel to the axes of theimpellers 2a and of such shape and dimensions that the metal'solidified in these grooves remains substantially stationary therein instead of passing into the die chamber 6B.. While in Figures 4 and 5 the grooves 4S are shown as extending as far as the die chamber, this is not necessarily the case, since, as the metal in them does not pass into the die chamber or does so at only a very slow rate, the grooves might be terminated at points such that they do not communicate with the chamber.

Figure 6 illustrates extrusion apparatus wherein the recesses complementary to the screw impeller 2b are constituted by a helical groove I8 of the same hand as the convolutions of the impeller. This gure also illustrates another feature of the invention, namely, that the chamber may be of steel with a cast-iron 'liner wherein the necessary grooves or recesses are formed. The cast iron may be strengthened by means of a steel sleeve which surrounds it and takes some of the operating strains, besides also serving to carry the cooling jacket or jackets when these are required. .As seen in Figure 6, the helical groove I8 is cut in a cast-iron liner I9 which is located within a steelbody 20, the members I9 and 20 together constituting the working chamber.

A source of non-uniformity in an extruded pipe may lie in the fact that,` as parts of the machine are at different temperatures, the expansion of the metal forming the body of the machine is not uniform and under some conditions distortion of the body may occur. 'I'his would have the eiect of displacing the ring die from its normal position concentric with the cone die, and consequently the pipe extruded would have a wall oi uneven thickness. To overcome this difficulty in the machine illustrated in Figure 6, the main ring die Hlm, similar to that depicted in Figure 1, is capable of slight movement in the radial direction when the nut I lb securing it has been slackened. Its position is then adjusted by means of set screws 2l threaded through the steel' body 20 and bearing at their inner ends on the outer periphery of the ring die lllfb. It is, of course, to be understood that, in addition to the two set screws shown in Figure 6, there would be at least two others also bearing on the ring die lUb and spaced at 90 or other appropriate angle from the set screws seen in the figure. Thus it is possible from time to time to adjust the position of the ring die so that it is perfectly concentric with its co-operating cone die.

The screw impeller is not necessarily of cylindrical form. For example, as shown in Figure '7,

the impeller 2c may be cylindrical along a portion of its length and of tapering form as the die chamber 6C is approached, the generatrix of the taper being a curved line. The shape of the internal surface of the working chamber is fashioned to correspond in general form to the tapered outline of the screw impeller. The clearance between the screw impeller an its complementary member may be varied along the screw to allow for the difference in temperascrew under operating conditions. Such a construction is shown in Figure 8, wherein it will be seen that over a portion of its length, lying between the points 22 and 23, the diameter of the working chamber is enlarged, so that there is a material clearance between those portions Vof its internal surface lying between the keyways and the helical projection 26 on the screw impeller. This gure also illustrates the feature that the screw impeller may be tapered at its forward end by graduated removal of the outer portion of the helical projection 2B thereon.

In the layout of apparatus illustrated in Figure 9, an extrusion machine 25 is shown as driven from an electric motor 26, through toothed gearing 2, a variable-speed gear box of any ordinary construction 28 and a'chain-drive 29. The motor 26 is connected to the supply mains 30 through the usual starting rheostat 3| and is provided with a speed regulator 32 in the eld circuit in the normal manner. A second rheostat 33 is, however, inserted in series with the starting rheostat 3l, the rheostat 33 being rated for continuous running and provided for the purpose of permitting the extrusion apparatus to be operated at a substantially reduced speed. In employing this apparatus, it is foundthat the load on the driving motor reaches a value characteristic for theitype of metal being extruded and that, as long as the temperature conditions of the machine remain steady, the current taken by the motor is substantially constant. It is possible, and actually very convenient, to judge the' operating conditions by observation of the motor current, as shown on an ammeter 34 linserted in the main circuit, which reflects temperature changes much more quickly than the thermometers associated with the machine. When the load on the motor increases, it indicates that the temperature of the machine has fallen and it is necessary to decrease the action of the cooling means until the load becomes normal again, and vice versa. An alternative method' of controlling the temperature in accordance with the motor load is to leave the cooling means unaltered and change the speed of the machine so as to increase or decrease the amount of metal passing through it, so varying the amount of heat brought into the machine, for example, an increase in the mof. tor load can be checked eventually by increasing slightly the speed of the machine, and vice versa. Automatic control may be readily applied.

If while the machine is working, for any reason it is necessary to stop quickly, then the metal in the screw impeller becomes united by solidication with the mass embedded in the cooperating member and great diiculty is experienced in starting the machine again unless the body 'of the machine is heated to about 300 C. just not necessarily be of the same kind as that which formsthe metal helix, for example, after operating the apparatus for a period with lead, it may be employed for the extrusion of a lead alloy, but

the grooves or recesses would remain lled with lead, although this might be very gradually replaced by the metal being extruded. Alternatively, the grooves or recesses may be permanently filled-with a material which will create the required friction with the metal to be extruded.

The output of the apparatus is approximately' proportional to the speed of revolution of the screw impeller up to a certain limiting output depending largely on thermal considerations involving the necessity of there being suicient time available during the passage through the apparatus of the lead or other metal to be exi truded forit to pass from the molten condition at the inlet to the plastic state soon after its entry to the working chamber and to the solid state up to the discharge end thereof.

The above described action of the apparatus i: i

helix being thus readily obtained. For example,

cooling means is required to keep the lead in the grooves or recesses chilled, so that it is sufliciently solidified to oier the requisite frictional re-t sistance to the relative movement between itself andthe lead in the helix. Further, when a large output is required from the machine, a large amount of heat must be absorbed, so that the metal maymakel the necessary changes in its state as it goes through the machine, and for this reason it may benecessary to cool the screw impeller.

The gradients of temperature all along" the machine must be suitably arranged for each metal or alloy to be extruded and, therefore, the above described means for heating and cooling are provided at the regions shown, viz: (a) v'heating means at the point of inlet of the metal to be extruded in order to maintain it in a molten con- 5 dition at a definite and constant temperature, (b) cooling jackets or other cooling means at the center of the machine, in order to control the temperature of the metal so that solidity may be maintained in that part of the machine in order to restrain the metal in the convolutions from rotation, and (c) heating means at the exit end of the machine in order, actually on extrusion, to control the temperature of the metal, which varies according to the production and the nature of the metal or alloy to be extruded.

Before the machine is operated all these regions are heated to establish predetermined temperatures in the various parts of the machine according to the type of metal or alloy to be extruded. Generally speaking, the heating element at the central portion of the machine is only used when starting to operate, particularly if metal has been allowed to solidify in the keyways and convolutions with the screw impeller stationary.

What I claim and desire to secure by Letters Patent of the United States ist- 1. Apparatus for extruding elongated metal bodies of constant cross-sectional design, Acomprising in combination inner and outer longitudinally extending and relatively rotatable concentric members, the outer of which forms the working chamber, a screw impeller formed on one of said membersV and the other of said members havi ing recesses of a formation designed to retain the said metal substantially stationary therein relatively to that in the convolutions of the impeller whereby the metal in the convolutions of the said impeller is sheared free from the metal in the recesses and advanced longitudinally of the impeller without turning.

2. Apparatus as in claim 1, characterized by the fact that the recesses are of draught-board form.

3. Apparatus as in claim 1, characterized by the fact that the recesses are constituted by helical grooves of the same hand as that of the convolutions of the impeller.

4. Apparatus as in claim 1, characterized by the fact that the vouter concentric member is made of steel fitted with a cast-iron liner.

5. Apparatus as in claim 1, characterized by the fact that the clearance between the screw impeller and its complementary member is varied along the screw.

6. Apparatus as in claim 1, characterized by the fact that the screw impeller is at least partially of tapering form the generatrix of which is a curved line and its complementary member is correspondingly shaped.

7. Apparatus as in claim 1, having a ring die and a cone die said ring die being radially adjustable relatively to said cone die, and set screws threaded thru said outer concentric member and bearing in a radial direction on said ring die.

8. Apparatus for extruding elongated metal bodies of constant cross-sectional design, comprising in combination inner and outer longitudinally extending and relatively rotatable concentric members, the outer of which forms the working chamber having an inlet for molten metal and an extrusion die, a screw impeller formed on one of said members and the other of said members having recesses coactive with and opening toward the convolutions of said impeller; said recesses being arranged and constructed to retain the metal therein substantially stationary relative to the metal in the convolutions of the impeller, heating means located in proximity to said inlet, and cooling means, constituted by a jacket for the circulation of a cooling medium, located between said inlet and said die. A

9. Apparatus as in claim 8, having heating means located in proximity to said die.

10. Apparatus asin claim 8, having heating means located between saidv inlet and said die.

11. Apparatus for extruding elongated metal bodies of constant cross-sectional design, comprising in combination inner` and outer longitudinally extending and relatively rotatable con-A centric members, the outer of which forms the working chamber having an inlet for molten metal and an extrusion die, a screw impeller formed on one of said members and the other of said members having recesses complementary to the convolutions of said impeller, said recesses being arrangedl and constructed to retain the metal therein substantially stationary relative to the metal in the convolutions of the impeller, heating means located in proximity to said inlet, and cooling means, constituted by a jacket for the circulation of a cooling medium, located between said inlet and said die, said recesses being in the form of longitudinal grooves extending substantially parallel to the axis of the screw impeller.

12. Apparatus for extruding elongated metal bodies of constant cross-sectional design, comprising an outer member formed to provide at least two working' chambers, a screw impeller dis.

posed longitudinally in each of said chambers and rotatable therein, said outer member having an inlet for molten metal and an extrusion die common to said chambers, the inner surfaces of said chambers having recesses therein complementary to the convolutions of said impeller, said recesses being arranged `and constructed to retain the metal therein substantially stationary relative to the metal in the convolutions of the impeller, heating means located in proximity to said inlet, and cooling means comprising a jacket for the circulation of a cooling medium about the area of the member between said inlet and said die.

13. Apparatus for extruding elongated metal bodies of constant cross sectional design, comthe metal in the recesses, said screw impeller having a chamber therein, and means for introducing f a cooling medium into and removing the same from' said chamber.

14. Apparatus for extruding elongated metal bodies of constant cross sectional design, comprising in combination inner and outer longitudinally extending and relatively rotatable concentric members, the outer of which forms the working chamber, a screw impeller formed on one of said members and the other of said members having recesses so constructed and arranged as to retain the said metal substantially stationary -metal in the recesses, and means for maintaining 5 dierent temperatures in various parts of the Working chamber for the purpose of maintaining the metal in such parts, respectively in the desired condition.

15. Apparatus for extruding elongated metal 10 bodies of constant cross sectional design, comprising in combination inner and outer longitudinally extending and relatively rotatable .concentric members, the outer of which forms the working chamber, a screw impeller formed on one 15 of said members and the other ofrsaid members having'recesss so constructed and arranged as to retain the said metal substantially stationary therein relatively `to that in the convolutions of the impeller whereby the metal in the convolu- 20 tions of the said impeller is sheared free from the metal in the recesses, and temperature regulating means for the working chamber comprising means for supplying heat thereto and a jacket therefor through which a cooling medium may be circulated.

16. Apparatus for extruding elongated metal bodiesof constant cross sectional design, comprising in combination inner and outer longitudinally extending and relatively rotatable concentric members, the outer of which forms the Working chamber, a screw impeller formed on one of said members and the other of said members having recesses so constructed and arranged as to retain the said metal substantially stationary therein relatively to that in the convolutions of the impeller whereby the metal in the convolutions of the said impeller is sheared free from the metal in the recesses,` and temperature regulating means constituted by means for the supply of heat and by at least one jacket through which a cooling medium may be circulated respectively concentrated at pointsat which heating and cooling of the apparatus is required.

ROBERT EUSTACE HORLEY. 

